This invention relates generally to jarring devices for fishing and the like and particularly to a jarring apparatus associated with well bore drill strings in order to dislodge the drill string if it becomes stuck in the well bore.
Hydraulically operated jarring devices for well bore fishing and drill strings are well known as disclosed for example in U.S. Pat. No. 3,729,058 and in my prior copending application. Ser. No. 605,057 filed Aug. 15, 1975, now abandoned. Generally in such jarring devices, an inner mandrel is displaced relative to an outer drill string to pressurize an annular body of fluid, the pressurized fluid being abruptly vented to release the mandrel for free travel to an impact position at which point the mandrel delivers a jarring blow to the drill string. By regulating the flow of fluid through a metering valve assembly as disclosed in my prior copending application aforementined, the duration of pressure build up and the intensity of the peak pressure may be adjusted to substantially constant values for each jarring cycle. The pressures developed in such jarring devices depend on the tension applied to the mandrel and the axial contraction of the annular pressure chamber formed between the mandrel and the drill string case. Such pressures are necessarily high if the impact produced on release of the pressure is to be of comparably high intensity.
It is therefore an important object of the present invention to provide a jarring apparatus through which the intensity of the impact is not dictated by the pressure induced in an annular body of fluid within the tool when an impact tension is applied and, therefore, may be tailored to other requirements.
A second important object of the present invention is to provide a jarring apparatus wherein the holding force exerted by a body of fluid pressurized to hold the mandrel and drill string case momentarily against movement relative to each other is applied radially and not axially.
A further important object of the present invention is to provide a jarring apparatus wherein the mandrel and drill string case are momentarily held against relative movement by mechanical engagement achieved by radial displacement of mechanical elements.
A still further object of the present jarring apparatus invention is to achieve rapid disengagement of the mechanical elements momentarily securing the mandrel and drill string case against relative movement with respect to each other by abruptly venting the body of pressurized fluid maintaining such engagement by appropriate valving mechanism and thereby permit relative movement between the mandrel and drill string case according to the tension applied.
Another object of the present invention is to eliminate the high pressure normally induced in the hydraulic fluids in prior devices.
Yet another object of the present invention is to achieve a jarring impact of greater intensity than normally obtainable with prior hydraulic jarring devices which use axially pressurized high pressure chambers.
Still another important object of the present invention is the isolation of the body of fluid pressurized to momentarily hold the mandrel and drill string against relative movement during application of a tension impact load from the fluid circuit generating the activating pressure so that release of the pressurized fluid can be controlled independently of the amount of tension impact load applied.
A further object of the present invention provides a jarring mechanism in which the jarring mechanism automatically immobilizes itself in the absence of a tensional impact load and the apparatus then operates as a telescoping joint.
Additional objects and advantages of the present invention will become apparent from the following descriptions together with the accompanying drawings.